At sea level, what is the approximate partial pressure of oxygen (O_2) in normal atmospheric air?

• A. 1.00 atm
• B. 0.03 atm
• C. 0.78 atm
• D. 0.21 atm

Answer: (D)

Verified step by step guidance

1. Understand that atmospheric air is a mixture of gases, primarily nitrogen (N_2), oxygen (O_2), argon (Ar), and trace gases. The total pressure at sea level is approximately 1.00 atm.
2. Recall that the partial pressure of a gas in a mixture is given by Dalton's Law of Partial Pressures: \(P_{gas} = X_{gas} \times P_{total}\), where \(X_{gas}\) is the mole fraction of the gas and \(P_{total}\) is the total pressure.
3. Identify the mole fraction of oxygen in normal atmospheric air, which is approximately 0.21 (or 21%).
4. Calculate the partial pressure of oxygen by multiplying the mole fraction of oxygen by the total atmospheric pressure: \(P_{O_2} = 0.21 \times 1.00\,\text{atm}\).
5. Interpret the result as the approximate partial pressure of oxygen in normal atmospheric air at sea level.